As a detergent for a contact lens in which particles are used as a polishing material, a detergent for a contact lens comprising a suspension of particles, which are insoluble in water, in an aqueous solvent such as a suspension of an inorganic material, such as silica or alumina in an aqueous solvent (Japanese Unexamined Patent Publication No. 6512/1981), a suspension of a cellulose in an aqueous solvent (Japanese Unexamined Patent Publication No. 159721/1985), or a suspension of an organic high molecular compound such as polyethylene or polysiloxane in an aqueous solvent, have been known. However, when these detergents are used, there is a necessity to pay attention to rinse the contact lens because particles insoluble in water remain on the surface of the contact lens if the contact lens is not sufficiently rinsed at the time of washing. In particular when a soft contact lens is washed, the particles tend to remain on the surface of the contact lens. Accordingly, the particles are not desirable in view of safety for eyes.
A detergent for a contact lens which is prepared by dispersing particles soluble in water such as sodium chloride or sodium hydrogencarbonate being pulverized to 50 to 200 mesh (mesh, the numerical value is based upon ASTM) as a substance soluble in water into an aqueous solvent when the detergent is used, has been known (specification of U.S. Pat. No. 4,588,444). The detergent has a merit that the preparation time is short. However, there is a necessity to disperse the particles into a solvent just before using the detergent because the particles gradually solve into the solvent, and the effect for washing is not fixed because the particles dissolve into the solvent just after the preparation of the detergent even though the detergent is prepared just before the use and the effect for polishing deteriorates. The combination of the particles soluble in water and an aqueous solvent has to be carried out by the user, and the ratio of the particles and the solvent is different depending upon each user. Accordingly, there is a defect that a large difference in the effect for washing generates among individuals.
In recent years, a detergent for a contact lens prepared by dispersing water-soluble fine particles having a particle diameter of 750 to 1 .mu.m into a nonaqueous water-miscible organic solution has been proposed (Japanese Unexamined Patent Publication No. 242916/1987). However, when the detergent is applied to a water-containing soft contact lens, there are some disadvantages that the lens is dehydrated by the organic solvent and is hardened and that the lens is swelled while the lens is dipped into the detergent for a long period of time. Further, the detergent has a difficulty to be practically used as a detergent for a water-containing soft contact lens because the lens cannot be worn on eyes if the washed lens is not dipped into an isotonic sodium chloride solution and the like for a long period of time.
In consideration of the actual circumstances of the above prior art, the purpose of the present invention is to provide a detergent for a contact lens which exhibits a large effect for washing, which is easily removed from a contact lens, and which does not injure a soft contact lens during washing and does not harden a water-containing soft contact lens.
The present inventors have eagerly investigated in view of the situation that prevention of hardening of a water-containing contact lens at the time of washing is particular important in order to accomplish the above-mentioned purpose. As a result, they have found that the hardening of the lens at the time of washing is caused by the following two factors. The factors are (1) increase of osmotic pressure caused by dissolving fine particles of water-soluble compounds into water at the time of washing, and (2) dehydration of a lens caused by a disperse medium to suspend fine particles of water-soluble compounds and interaction of the disperse medium and the lens.
The present inventors have investigated to remove these factors. As a result, they have found a detergent having no risk of hardening a lens during washing when salt value and solubility in water are adjusted as to the above point (1), and when a composition of which major component is an aqueous dispersion of a gel prepared by the reaction of a mixture of an acrylic acid compound having a cross-linking site as a disperse medium and a polyhydric alcohol is used, and a paste having a high concentration of the water-soluble compound fine particles prepared by mixing the water-soluble compound fine particles of which salt value and solubility are adjusted with the above-mentioned disperse medium is used as to the above point (2), and they have accomplished the present invention.